Author

Abstract

The temperature dependence of the Mossbauer spectra of the iron(III) trisdithiocarbamate complexes, Fe(R2dtc)3, where R represents N,N'-disubstitution with methyl, ethyl, isopropyl, benzyl, n-hexyl and cyclohexyl groups, has been measured from 1.3 or 4.2 K to room temperature. A consideration of these spectra in terms of spin-state relaxation indicates that the hyperfine parameters for the high-spin and low-spin states at equilibrium in some of these complexes must be quite similar. The Mossbauer absorption area shows a strong temperature dependence, which has been analysed with the Debye model. At lower temperatures the spectra show broad asymmetric linewidths, which result from the onset of slow paramagnetic relaxation on the Mossbauer timescale. An analysis of the observed Mossbauer spectral lineshape with either a Blume or Bradford and Marshall relaxation profile indicates that the paramagnetic relaxation is almost isotropic in Fe((methyl) 2dtc)3, has a larger transverse than longitudinal component in Fe((benzyl)2dtc)3 and is predominantly transverse in Fe((ethyl)2dtc)3 and Fe((cyclohexyl) 2dtc)3. Below 90, 40, 25 and 15 K for the methyl, ethyl, benzyl and cyclohexyl derivatives, respectively, the paramagnetic relaxation rate is independent of temperature and dominated by a spin-spin relaxation mechanism. Above these temperatures the paramagnetic relaxation is dominated by a two-phonon spin-lattice relaxation mechanism.